Failsafe actuator

ABSTRACT

A failsafe actuator for returning an actuator driven element to a failsafe position in case of a failure condition is provided. The failsafe actuator may include mechanical or electrical means to provide a failsafe function. Such a failsafe actuator may be used in a stabilizer bar system of a vehicle to ensure that at least one stabilizer bar is returned to a failsafe or engaged condition should a failure condition occur when the stabilizer bar is disengaged. Various failure conditions can include loss of electrical power to the actuator or some internal actuator failures.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/267,090, filed Jul. 19, 2002, which claims the benefit of the filingdate of U.S. Provisional Patent Application Ser. No. 60/306,628, filedJul. 19, 2001, the teachings of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to an actuator with a failsafemechanism for permitting an actuator to move an actuator driven element,and in particular a vehicle stabilizer bar, to a safer default positionin case of a failure condition such as an external or internalelectrical failure.

BACKGROUND OF THE INVENTION

Vehicles, especially four wheel drive and off-road vehicles, may beequipped with a vehicle suspension system which includes a stabilizerbar or stabilizer bars (one for the front and one for the rear).Generally, a stabilizer bar includes a torsion bar that links two wheelstogether so they act in unison at high speed. For example, thestabilizer bar enhances drivability on smooth road surfaces by resistinginstability as a vehicle changes lanes. On the other hand, the same highrigidity imparted by the stabilizer bar may degrade traction andindependent wheel articulation on rough off-road surfaces. In addition,the high rigidity of the stabilizer bar may cause the traction of theleft side and right side wheels to differ significantly causingdifferential transmission of driving torque which may further degraderoad handling characteristics on rough road surfaces. Therefore, astabilizer bar disconnect system driven by an actuator may be used todeactivate the stabilizer bar when driving on rough road conditions.

However, if failures such as external actuator electrical or internalactuator electrical failures occur, the actuator may become stuck in an“off-road” position with the stabilizer bar deactivated. This “off-road”position is undesirable for most smooth road driving conditions. Hence,reduced drivability could lead to a greater likelihood of accidents suchas rollovers on smooth road conditions until the failure problem isrepaired.

Accordingly, there is a need in the art for an actuator with a failsafemechanism for controlling an actuator driven element, particularly astabilizer bar mechanism in a vehicle, which permits return of theactuator driven element to a more safe default position in case of afailure condition such as an external or internal electrical failure.

BRIEF SUMMARY OF THE INVENTION

A failsafe actuator for returning an actuator driven element to afailsafe position in case of a failure condition consistent with theinvention includes: a drive assembly configured to drive the actuatordriven element, the drive assembly including a plunger having at least afirst plunger position, the actuator driven element responsive to theplunger such that the actuator driven element is in the failsafeposition when the plunger is in the first plunger position; a returnmechanism; and an electromechanical mechanism configured to hold theplunger in at least a second plunger position and further configured torelease the plunger upon detection of the failure condition therebypermitting the return mechanism to drive the plunger to the firstplunger position and hence the actuator driven element to the failsafeposition.

Another failsafe actuator for returning an actuator driven element to afailsafe position in case of a failure condition consistent with theinvention includes: a drive assembly configured to drive a plunger froma first plunger position to a second plunger position; a returnmechanism configured to drive the plunger from the second plungerposition to the first plunger position, the actuator driven elementresponsive to the plunger such that the actuator driven element is inthe failsafe position when the plunger is in the first plunger position;and an electromechanical mechanism configured to hold the plunger in atleast the second plunger position and further configured to release theplunger upon detection of the failure condition thereby permitting thereturn mechanism to drive the plunger to the first plunger position andhence the actuator driven element to the failsafe position.

Another failsafe actuator for returning an actuator driven element to afailsafe position in case of a failure condition consistent with theinvention includes: a drive assembly configured to drive the actuatordriven element, the drive assembly including an electrical motor; and anelectrical energy storage element coupled to the electrical motor, theelectrical energy storage element providing sufficient electrical energyto the electrical motor to enable the electrical motor to drive theactuator driven element to the failsafe position upon detection of afailure condition.

Another failsafe actuator for returning an actuator driven element to afailsafe position in case of a failure condition consistent with theinvention includes: a drive assembly for driving the actuator drivenelement; and an energy storage element in working relationship with thedrive assembly, the energy storage element configured to providereplacement energy to drive the actuator driven element to the failsafeposition in case of the failure condition.

A method for returning an element to a failsafe position in case of afailure condition consistent with the invention includes the steps of:driving a plunger from a first plunger position to a second plungerposition; holding the plunger in at least the second plunger position;detecting the failure condition; releasing the plunger from the at leastsecond plunger position upon detection of the failure condition; anddriving the plunger from the at least second plunger position to thefirst plunger position, the element responsive to a position of theplunger such that the element is in the failsafe position when theplunger is in the first plunger position.

Another method for returning an element to a failsafe position in caseof a failure condition consistent with the invention includes the stepsof: driving the element from an electrically powered drive source;storing electrical energy in an electrical energy storage element;detecting the failure condition; and providing the energy from thestorage step to the electrically powered drive source to drive theelement to the failsafe position upon detection of the failurecondition.

Another method for returning an element to a failsafe position in caseof a failure condition consistent with the invention includes the stepsof: storing energy; detecting the failure condition; and utilizing theenergy from the storing step to return the element to a failsafeposition.

A stabilizer bar system consistent with the invention includes: at leastone stabilizer bar; a power source; an actuator receiving electricalpower from the power source, the actuator comprising: a drive assemblyconfigured to drive the at least one stabilizer bar, the drive assemblyincluding a plunger having at least a first plunger position, the atleast one stabilizer bar responsive to the plunger such that the atleast one stabilizer bar is in the failsafe position when the plunger isin the first plunger position; a return mechanism; and anelectromechanical mechanism configured to hold the plunger in at least asecond plunger position and further configured to release the plungerupon detection of the failure condition thereby permitting the returnmechanism to drive the plunger to the first plunger position and hencethe at least one stabilizer bar to the failsafe position.

Another stabilizer bar system consistent with the invention includes: atleast one stabilizer bar; a power source; an actuator receivingelectrical power from the power source, the actuator including: a driveassembly configured to drive the at least one stabilizer bar, the driveassembly comprising an electrical motor configured to receive power fromthe power source; and an electrical energy storage element coupled tothe electrical motor and the power source, the electrical energy storageelement providing sufficient electrical energy to the electrical motorto enable the electrical motor to drive the at least one stabilizer barto a failsafe position upon detection of a failure condition.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will be apparent from the followingdetailed description of exemplary embodiments thereof, which descriptionshould be considered in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a simplified plan view of a vehicle having an exemplaryactuator consistent with the present invention for driving a stabilizerbar of the vehicle;

FIG. 2 is a simplified block diagram of an exemplary control systemincluding an actuator consistent with the present invention forcontrolling the stabilizer bar system of FIG. 1;

FIG. 3 is a simplified block diagram of an exemplary actuator consistentwith the present invention having a mechanical failsafe system shown ina failsafe position;

FIG. 4 is a simplified block diagram of the exemplary actuator of FIG. 3in a non failsafe position;

FIG. 5 is a simplified block diagram of another exemplary actuatorconsistent with the invention having an electrical failsafe systemincluding an electrical energy storage element; and

FIG. 6 is an exemplary circuit diagram of the actuator of FIG. 5.

DETAILED DESCRIPTION

The present invention relates generally to an actuator with a failsafemechanism for permitting an actuator to move an actuator driven elementto a more safe default position in case of a failure condition such asan external or internal electrical actuator failure. The presentinvention is described with reference to an actuator for activating anddeactivating a stabilizer bar system in a vehicle. Those skilled in theart, however, will recognize that an actuator consistent with thepresent invention may be utilized in a host of other environments. Thus,it is to be understood that the present invention is not limited to theillustrated exemplary embodiments described herein. Rather, the presentinvention may be incorporated in a wide variety of actuators, andactuator systems and devices without departing from the spirit and scopeof the present invention.

Turning to FIG. 1, a simplified plan view of an exemplary vehicle 100having actuator activated stabilizer bars 110 a, 110 b is illustrated.The stabilizer bars 110 a, 110 b may be coupled to either the frontwheels 120, 122 or rear wheels 124, 126 respectively through a pair ofsuspension links 116, 118. The stabilizer bars 110 a, 110 b may befurther coupled to the body of the vehicle by a pair of brackets 112,114. Those skilled in the art will recognize a variety of means forcoupling the stabilizer bars 110 a, 110 b to the f wheels and to thevehicle 100.

An actuator 102 consistent with the present invention may be coupled toone or both stabilizer bars 110 a, 110 b at a mid-point between thefront wheels 120, 122 or the rear wheels 124, 126 for driving thestabilizer bar system into an activated and deactivated position.However, those skilled in the art will recognize a variety ofconfigurations for coupling an actuator to one or both stabilizer bars.For example, the actuator may be located closer to the wheels or at anypoint along the stabilizer bars 110 a, 110 b. The actuator may also notbe coupled to the stabilizer bars 110 a, 110 b directly, but rather tosome driving means to drive the stabilizer bars 110 a, 110 b.

A controller 104 may provide control signals to the actuator 102 to movethe stabilizer bars 110 a, 110 b into either an activated or deactivatedstate. An activated state would typically be for most driving conditionson smooth road surfaces, while a deactivated state would be for roughroad surfaces at low speed. The controller may be responsive to anoperator input, an input from another one of the vehicle controlmodules, or a sensor 106 for sensing the current type of road condition.A variety of such sensors, and positions for locating such sensorswithin the vehicle, are known to those skilled in the art. For example,one such sensor may be adapted to transmit ultrasonic waves towards theroad surface and to receive or detect the ultrasonic waves reflectedback by the road surfaces. Judging the variation of the received signalsover time and comparing them to a predetermined range enables the sensorto determine if the road surface is rough or smooth. Other sensors mayuse light or laser beams.

A power source 108 provides electric power to the actuator 102. Thepower source may be any number of power sources including a vehiclebattery or any part of the vehicle's electrical system driven by thealternator when the vehicle's motor is running.

In general, and with reference to the exemplary block diagram controlsystem of FIG. 2, there are multiple ways to signal the stabilizer barengagement system 206. One way is with a sensor 106. The sensor 106senses when the vehicle is on a smooth or rough road surface and sendsassociated signals to the controller 104. Another way to signal thesystem is by operator command 202. The operator may elect to send asignal to the controller 104 through a switch. Yet another way to signalthe controller is through any variety of the other vehicle controlsystems 204.

Once the controller 104 receives a signal from one of the varioussources 106, 202, it may then confirm that all conditions areappropriate through communication with other vehicle systems. Thecontroller 104 then, in turn, provides signals to the actuator 102 todeactivate or activate the stabilizer bar system 206 as desired. Forinstance, if an operator desires an off-road state the actuator 102would deactivate the stabilizer bar system 206, or if the operatordesired a normal operating mode the actuator 102 would activate thestabilizer bar system 206.

Advantageously, an actuator 102 consistent with the present inventionincludes a failsafe mechanism to ensure that the stabilizer bar system206 is driven to its failsafe, or activated position, in case of afailure condition such as an interruption in power from the power source108 or an internal electrical failure in the actuator 102.

Turning to FIG. 3, a simplified block diagram of an exemplary failsafeactuator 300 having a mechanical failsafe mechanism is illustrated. Theactuator 300 is in a position that corresponds to a failsafe positionfor an actuator driven element (not shown). The actuator 300 includes adrive assembly 303 configured to drive an actuator driven element suchas a stabilizer bar or stabilizer bar system. The drive assembly 303 mayinclude a motor 306 with an output shaft 308, a gear train 314, and aplunger 318.

The gear train 314 may include a set of reduction gears 310, e.g., aplanet gear arrangement. The gear train 314 may also include a lostmotion device 312, e.g., a clutch. The gear train 314 may be coupled toa plunger 318 to drive the plunger axially. The plunger may also berotated or driven in other directions. The plunger may be driven againsta return mechanism 316, e.g., a compression spring.

As described more fully with reference to FIG. 4, an electromechanicalmechanism 323 may also be provided to mechanically link to the actuatordrive elements such that it can impede actuator output motion. Forinstance, one example of an electromechanical mechanism 323 is asolenoid 320 with a solenoid output shaft 322. The solenoid shaft 322may be located perpendicular to the axially driven plunger 318. Thesolenoid 320 may also be controlled by a control signal through aseparate control path 331 than the control path 333 for the motor 306.

Turning to FIG. 4, a simplified block diagram of the exemplary actuatorof FIG. 3 in a non-failsafe position is illustrated. In a stabilizer barsystem, the actuator position of FIG. 4 would result in a stabilizer bardisengaged position. For clarity, like parts from prior figures arerepresented by like numerals.

In operation, a signal (e.g., from sensor 106 or from operator input202) is provided to the controller 104 to disengage the stabilizer barsystem. The controller 104, in turn, provides a control signal to themotor 306 via control path 333. The output shaft 308 of the motor drivesthe plunger 318, through the gear train 314, axially away from the motorcausing the return mechanism 316, e.g., a compression spring, tocompress. The solenoid shaft 322 extends axially upward perpendicular tothe axially extending plunger 318. The motor 306 may then be turned offwhile the plunger 318 and return mechanism 316 are held in a stabilizerbar disengaged position by the solenoid shaft 322.

The plunger 318 may be held until the controller 104 provides a propercontrol signal indicating smooth road conditions and triggering theplunger to return to its failsafe position of FIG. 3. In addition, afailure condition would also trigger return of the plunger 318 to thefailsafe position of FIG. 3. For instance, the plunger may be held inits retracted position as long as a small holding current is applied tothe solenoid 320 by the power source 108. In case of an external orinternal electric failure causing interruption of the holding current,the solenoid output shaft 322 would self-retract to a retractedposition. Such self-retraction force of the solenoid shaft 322 may beprovided by an internal solenoid compression means, e.g., compressionspring.

The return mechanism 316 biased against the plunger 318 may provideaxial force in a direction back towards the motor. Advantageously, ifnecessary, the lost motion device 312, e.g., a clutch, may also be inits released position thereby aiding the return mechanism 316 to backdrive the plunger against the gear train 314 with less force. As such, afailsafe mechanism is provided to back drive the plunger to its failsafeposition of FIG. 3 in case of a failure condition such as an external orinternal electric power failure.

In designing and choosing a return mechanism 316 and electromechanicalmechanism 320, the retraction force of the electromechanical mechanism,e.g., the retraction force of the solenoid output shaft 322, should begreater than the frictional forces induced by return mechanism. Theretraction mechanism 316 should also provide enough force to back drivethe plunger 318 against the gear train 314. Again, the use of the lostmotion device, e.g., clutch 312, may enable this to occur with a modestretraction mechanism exhibiting less force. If there is no clutch, theretraction mechanism 316 should provide a greater force than if there isa clutch. The clutch is optional depending on the particulars of thesystem including the desired retraction mechanism and its associatedretraction force.

Turning to FIG. 5, a simplified block diagram system 500 of anotherexemplary actuator 502 consistent with the invention having anelectrical failsafe system including an electrical energy storageelement 509 is illustrated. In operation, the power source 508 normallyprovides power to the electrical motor 506 of the drive assembly 503.The drive assembly 503 in turn drives the actuator driven element 510.When the power source 508 is normally available, it serves to alsocharge the electrical energy storage element 509. Such element 509 maybe any variety of devices known in the art for storing electric energy,e.g., a rechargeable battery, a capacitor, an inductor, and the like.Such element should be sized appropriately to provide sufficientelectrical energy to the motor 506 such that the actuator driven element510 may be driven to a failsafe position upon detection of a failurecondition. For instance, such a failure condition may be loss of powerfrom the power source 508 to the motor 506.

Turning to FIG. 6, one exemplary circuit diagram for the actuator ofFIG. 5 is illustrated. Those skilled in the art will recognize a varietyof circuit configurations and electrical energy storage elements thatmay be used without departing from the scope of the present invention.The electrical energy storage element of FIG. 6 is a capacitor 602. Thecapacitor 602 should be large enough to provide sufficient electricalenergy to the motor 606 to provide for a single actuation underworst-case conditions. For one exemplary capacitor 602, this wouldrequire a capacitor of 1 Farad at−40 degrees Celsius capable of beingcharged to 15 volts. A plurality of zener diodes 604, 606, 608 may alsobe provided to direct current flow to the capacitor 602 under normalcharging conditions and from the capacitor under failsafe operationconditions.

The embodiments that have been described herein, however, are but someof the several which utilize this invention and are set forth here byway of illustration but not of limitation. It is obvious that many otherembodiments, which will be readily apparent to those skilled in the art,may be made without departing materially from the spirit and scope ofthe invention as defined in the appended claims.

1. A vehicle stabilizer bar system comprising: at least one vehiclestabilizer bar; and an actuator comprising: an output member; anelectric motor operatively coupled to said output member for moving saidoutput member from a first position to a second position uponenergization of said electric motor by a power source, said vehiclestabilizer bar being responsive to said output member such that vehiclestabilizer bar is in a first stabilizer bar state when said outputmember is in said first position and is in a second stabilizer bar statewhen said output member is in said second position; and at least oneelectrical energy storage element coupled to said electric motor, saidelectrical energy storage element being configured for energizing saidmotor to move said output member from said second position to said firstposition upon interruption of power from said power source to saidmotor.
 2. The system of claim 1, wherein said output member comprises aplunger.
 3. The system of claim 1, wherein said electric motor comprisesa drive shaft, and wherein said electric motor is operatively coupled tosaid output member through a gear train coupled to said drive shaft. 4.The system of claim 1, wherein said electrical energy storage elementcomprises a capacitor.
 5. The system of claim 4, wherein said capacitorhas a value of at least one Farad.
 6. The system of claim 1, whereinsaid first stabilizer bar state is an engaged state of said stabilizerbar and said second stabilizer bar state is a disengaged state of saidstabilizer bar.